The responses of plants and other life forms, such as yeasts, to salt (sodium chloride) and other environmental stresses have been studied extensively for many years. Certain plants and yeasts have been identified as being more "salt tolerant" than others and it has long been hypothesized that such plants and/or yeasts must contain within their genomes at least one gene which is capable of transporting sodium into or out of the cellular structure of the organism. However, after years of study, no such single gene or gene product directly involved in Na.sup.+ or Cl.sup.- metabolism has heretofore been identified (Mechanisms of Salinity Tolerance in Plants, T.J. Cheeseman Plant Physiol (1988) 87, 544-550).
Identification and characterization of any such gene or gene product which confers salt tolerance is, of course, of immense commercial potential, regardless of the species in which it is identified. Modern genetic engineering techniques may be employed to transfer the gene to any desired species in which it will be reliably expressed thus raising the possibility of cultivating crops in arid or semi arid areas using saline waters for irrigation purposes, or for producing crops in areas of increasing salinity, such as the coastal plains of California. If a salt tolerant gene is inserted into a yeast, such as brewers yeast, it should be possible to produce ethanol with water or feedstocks having significant salinity--a condition which pertains in many areas of the world.